1. Field of the Invention
The present invention relates to an apparatus and method for detecting a pilot signal in a mobile communication system. More particularly, the present invention relates to an apparatus and method for detecting a pilot signal in a mobile communication system that are capable of detecting whether a secondary/auxiliary pilot signal is transmitted in a mobile communication system based on the CDMA 2000 standard.
2. Description of the Related Art
In general, in order to perform communication in a mobile communication system, a channel is established and data is transmitted and received over the channel. Such a channel should be configured to have a different transmission power depending on a position of a mobile terminal with respect to a base station. That is, a mobile terminal far from a base station should transmit data at higher power than a mobile terminal near the base station, such that the base station can normally receive the data.
As such, control of transfer power from the base station to the mobile terminal is referred to as forward link power control. Conversely, control of transfer power from the mobile terminal to the base station is referred to as reverse link power control.
The base station can control reverse link power only when it knows a state of the channel through which data is received from the mobile terminal. That is, in order to perform synchronization detection, it is necessary to know a state of the channel through which received signals have passed. Information on such a channel state can be provided through a pilot channel.
However, a general mobile communication system performs only forward link power control.
Accordingly, the CDMA 2000 standard, which is currently adopted as a synchronous IMT 2000 system standard, uses the pilot signal even in the reverse link. Accordingly, the base station can perform synchronization detection, and thus, reverse link data transmission can be smoothly performed and system capacity can be improved.
The channel state is detected in a channel estimator using data transmitted through the pilot channel, and a signal distortion level is estimated through the channel estimation. Further, information distortion can be reduced by applying the estimation value to received information bit correction.
In the CDMA 2000 standard, high-speed data transmission is supported through a reverse traffic channel, and a primary pilot together with a secondary/auxiliary pilot is transmitted in order to increase the efficiency of power control and channel estimation.
The secondary/auxiliary pilot in the CDMA 2000 standard is characterized in that when transmitting data at high speed, it transmits data with greater power than the primary pilot in order to increase channel estimation efficiency.
The secondary/auxiliary pilot is not always transmitted but rather is discontinuously transmitted depending on a data transmission rate of traffic to be transmitted from a transmitter.
Channel estimation is performed using only the primary pilot signal when there is only a primary pilot signal, and is performed using a combined signal of the primary pilot signal and secondary/auxiliary pilot signal when there is a secondary/auxiliary pilot signal.
Accordingly, only when it is correctly determined whether the secondary/auxiliary pilot signal is present can channel estimation performance be improved by enhancing a signal to noise ratio of an input signal used in the channel estimation.
Generally, a receiver determines whether the secondary/auxiliary pilot signal is present or not by observing energy (or power) of the secondary/auxiliary pilot signal for a predetermined time interval. Since channel estimation is performed after determining whether the secondary/auxiliary pilot signal is present or not, the traffic channel signals should be stored in a buffer until a determination is made.
Below, a conventional secondary/auxiliary pilot signal detection apparatus of a mobile communication system will now be described with reference to FIG. 1.
FIG. 1 is a schematic block diagram of a conventional pilot signal detection apparatus.
Referring to FIG. 1, the pilot signal detection apparatus comprises an accumulator 10, an energy detector 11, and a comparison and determination unit 12.
When a signal transmitted from a transmitter passes through a mobile channel environment and is received in the form of a pilot symbol to which a noise component is added, the accumulator 10 accumulates the received pilot symbols for a predetermined time interval and then provides them to the energy detector 11.
The energy detector 11 detects an energy value for the pilot symbols provided from the accumulator 10 and provides the detected energy value to the comparison and determination unit 12.
The comparison and determination unit 12 compares the energy value for the pilot symbols provided from the energy detector 11 with an established threshold value, and then determines whether the secondary/auxiliary pilot signal is present based on the comparison results.
Operation of a secondary/auxiliary pilot signal detection apparatus having such a configuration will now be briefly explained.
First, a signal symbol transmitted from the transmitter passes through a mobile channel environment and is received in a receiver together with an additional noise component. Such received signals are accumulated in the accumulator 10 for a predetermined time interval and then provided to the energy detector 11.
The energy detector 11 detects the energy of the symbols provided from the accumulator 10. When there is no secondary/auxiliary pilot signal, the measured energy Eaux is given by Equation (1) below:Eaux=naux  [Equation 1]wherein naux is a noise component.
In contrast, when there is a secondary/auxiliary pilot signal, the measured energy Eaux is given by Equation (2) below:Eaux=Paux+naux  [Equation 1]wherein Paux is the secondary/auxiliary pilot signal and naux is a noise component.
When detecting energy given by Equations (1) and (2), the detected energy is used to determine whether the secondary/auxiliary pilot signal is present or not in the comparison and determination unit 12 using Equation (3) below:Decision=Eaux>TH  [Equation 3]
That is, it is determined that the secondary/auxiliary pilot signal is present in the received signal when the energy value detected in the energy detector 11 is greater than an established threshold value TH, and it is determined that the secondary/auxiliary pilot signal is not present in the received signal when the energy value detected in the energy detector 11 is smaller than the threshold value TH.
Here, the threshold value TH is a boundary value determined in consideration of a distribution of a noise signal and the secondary/auxiliary pilot signal.
As such, in order to reliably gauge whether the secondary/auxiliary pilot signal is present or not in the manner described above, observation for a predetermined time interval is required. However, since channel estimation is performed after it is determined whether the secondary/auxiliary pilot signal is present or not, the traffic channel signals should be stored in the buffer until a determination is made. Therefore, as the time interval for measuring energy increases, the amount of data to be stored increases and process delay times also increase.
Accordingly, a need exists for a system and method for reducing detection delay times in a receiver, thereby also reducing the size of buffers for storing traffic channel signals.